1. Field of the Invention
The present invention relates to the production of slide fasteners, and more particularly to a method of and an apparatus for forming an element-free space section in a pair of continuous concealed-slide-fastener stringers.
2. Prior Art
A number of devices for the purpose described above are known in which a chain of interengaged filamentary coupling elements attached by sewn stitches to a pair of continuous tapes along their folded inner longitudinal edges is cut for a length corresponding to the length of an element-free space section by means of a punch and a die. It has been a common practice to this end that the tapes are pulled apart locally in order to allow the punch to enter between the adjacent tape edges so that the cutting of the coupling elements is accomplished without cutting the tapes. However, pulling the tapes locally would often make the tapes to become unrecoverably deformed or otherwise damaged. Further, due to this tape pulling, an increased rate of production with the prior apparatus is difficult to achieve. Such prior art is exemplified by U.S. Pat. No. 3,225,430, issued Dec. 28, 1965, and French Pat. No. 1,561,401, issued Mar. 28, 1969.
A solution has been proposed by Japanese Utility Model Publication (Jikkosho) 51-4802, in which a guide member having a tapering forward end portion is employed to force the adjacent folded tape edge portions apart to expose head portions of a series of the interengaged coupling elements. A punch is moved toward a die through a rectangular opening in the guide member to cut the exposed head portions of the coupling elements supported on the die. However, since it is necessary to force the guide member against the coupling elements continually, high-speed feeding of the fastener stringers through the apparatus cannot be achieved, and the coupling elements can be easily damaged by the guide member. Further, in this prior apparatus, the head portions of the coupling elements are only cut with the leg portions remaining on the folded tape edges and, therefore, it is impossible to form a space section perfectly free from any coupling element piece.